Interferometer using transverse deviation of test beam

Abstract

A laser interferometer 10 uses light divided into reference beam 14 and test beam 15 traveling different paths from which beams 14 and 15 are reflected and recombined for detecting interference fringes. The path for test beam 15 is arranged to change in length with deviation transverse to its path. To do this, a reflective diffraction grating 25 is inclined relative to test beam 15 at the autocollimation angle of the grating to reflect the test beam back on itself from the inclined surface of the grating. Then transverse deviation of the region where test beam 15 is incident on grating 25 changes the path length of the test beam reflected from the inclined surface of the grating and allows a measurement.

I claim: 
     
       1. An interferometer using light divided into reference and test beams traveling different paths from which said beams are reflected and recombined for detecting interference fringes, the path for said test beam being arranged to change in length with deviation transverse to said test beam path, said interferometer comprising: a. a test beam reflector formed as a reflective diffration grating;   b. said diffraction grating being inclined relative to said test beam at the autocollimation angle of said grating so said grating reflects said test beam back on itself;   c. means responsive to said deviation transverse to said test beam path for moving the region where said test beam is incident on said inclined grating; and   d. said inclination of said diffraction grating being oriented relative to said test beam so that movement of said region where said test beam is incident on said inclined grating changes the path length of said test beam.   
     
     
       2. The interferometer of claim 1 wherein said autocollimation angle is about 45° or more. 
     
     
       3. The interferometer of claim 1 including means for moving said grating transversely of said test beam in correspondence with a deviation to be measured. 
     
     
       4. The interferometer of claim 1 including means for moving said test beam transversely of said grating in correspondence with a deviation to be measured. 
     
     
       5. The interferometer of claim 1 wherein a telescope is arranged for moving along a line parallel with said test beam path while said test beam passes through said telescope to measure said line for deviation transverse to said test beam path. 
     
     
       6. The interferometer of claim 1 including angularly movable means in the path of said test beam for moving said test beam transversely of said grating to measure angular deviation. 
     
     
       7. The interferometer of claim 1 wherein a reflector for said reference beam is arranged in the region of said grating so that said reference and test beams are approximately parallel and of approximately equal lengths. 
     
     
       8. The interferometer of claim 7 wherein said reference beam reflector and said grating are mounted for movement together along a line parallel with said test beam path to measure said line for deviation transverse to said test beam path. 
     
     
       9. The interferometer of claim 7 wherein said autocollimation angle is about 45° or more. 
     
     
       10. The interferometer of claim 7 including means for moving said grating transversely of said test beam in correspondence with a deviation to be measured. 
     
     
       11. The interferometer of claim 7 including means for moving said test beam transversely of said grating in correspondence with a deviation to be measured. 
     
     
       12. The interferometer of claim 11 wherein said movable means is a telescope arranged for moving along a line parallel with said test beam path while said test beam passes through said telescope to measure said line for deviation transverse to said test beam path. 
     
     
       13. The interferometer of claim 11 wherein said movable means is an angularly movable element in the path of said test beam for moving said test beam transversely of said grating to measure angular deviation.